1. Field of the Invention
The invention is a process for electrolytically depositing chromate films on metallic surfaces.
2. Background of the Invention
Chromate films are extensively used in a variety of industrial applications including as corrosion protection and as a film to increase adherence of organic coatings to metallic surfaces. Typical chromating procedures are described in a variety of references including "Chromate Conversion Coatings" by F. W. Eppensteiner and M. R. Jenkins in Metal Finishing, September 1975, page 29; "A Study of Surface Chromium on Tinplate" by S. E. Rauch, Jr. and R. N. Steinbicker, in Journal of Electrochemical Society, Vol. 120, No. 6, June 1973, Page 735; and, U.S. Pat. No. 3,625,844 issued to Walter A. McKean. Chromating procedures are also described by H. N. Vazirani in U.S. Pat. No. 3,632,389, issued Apr. 3, 1968.
These procedures generally use a 5 percent solution of potassium dichromate or an acidic aqueous solution of chromium trioxide. Although these procedures work well in many applications, it is often desirable to have chromate films which exhibit added corrosion protection greater adhesive qualities or other superior characteristics. For example, chromate films are used as masks for gold electroplating. It is desirable to use more vigorous conditions (higher temperatures, higher current densities, etc.) for gold plating to insure better gold adhesion and more rapid electroplating. With more effective chromate masks, gold electroplating could be carried out under more vigorous conditions without endangering the masking properties of the chromate film toward gold plating.